Cognition is dependent upon the proper formation of neural circuits and the adaptations of those circuits in response to experience. The cellular and molecular mechanisms underlying declarative learning and memory constitute a predominant area in basic neurobiological research and are of considerable clinical relevance. Dysregulation of the biochemical mechanisms underlying cognition likely contributes to neurodevelopmental and neurodegenerative disorders including autism, Alzheimer's, mental retardation, schizophrenia, and attention deficit and hyperactivity disorder. We have focused on synaptic signal transduction mechanisms involving the neuronal protein kinase Cdk5, with the goal of determining its role in learning and memory. We developed an innovative transgenic approach that allowed the induction of knockout of the neuronal protein throughout the brain of adult mice. This led to the discovery that the neuronal protein kinase Cdk5 governs synaptic plasticity, learning, and memory. We found that this was due to changes in the levels and surface expression of the NR2B subunit of the NMDA receptor. Here we propose to characterize the interactions between Cdk5 and NR2B, evaluate the role of Cdk5-NR2B interactions in synaptic plasticity, and assess the role of Cdk5-NR2B interaction in learning, and memory. The proposed studies are based on our preliminary findings that Cdk5 phosphorylates NR2B at a novel site and this phosphorylation controls the translocation of the receptor to the synaptic cell surface. We will characterize the regulation of this important site with regard to phosphorylation/dephosphorylation and define its physiological function. We hypothesize that the phosphorylation state of NR2B is dynamically regulated during learning and essential for consolidation of memory in the hippocampus. Furthermore, we show that are developing small drug-like interfering peptides based that disrupt Cdk5-NR2B interactions in vitro and in vivo. We will use this selective targeting approach to manipulate Cdk5-NR2B interactions and bidirectionally control the phosphorylation state and surface levels of NR2B. This will allow us to modulate synaptic plasticity, learning and memory in the hippocampus. Thus by combining advanced transgenic, biochemical, neurophysiological and behavioral approaches, we will define an important new mechanism that mediates cognition and demonstrate it as a target for the possible development of innovate disruption strategies to treat cognitive disorders.